Abstract The eventual goal of this line of research is to determine whether, and through what mechanisms, Animal- Assisted Therapy (AAT) is beneficial for the treatment of maltreated youth. The current project is a feasibility study to determine if larger clinical trials are warranted. The specific aims of the current study are (1) to examine whether the integration of AAT into standard Trauma-Focused Cognitive-Behavioral Therapy (TF- CBT) enhances treatment effectiveness, (2) to evaluate the tolerability and feasibility of AAT when integrated into TF-CBT, and (3) to evaluate hypothesized mediational processes that may explain observed positive effects for the integration of AAT. Maltreated youth may display myriad emotional and behavioral symptoms; prominent among these is posttraumatic stress (PTS). TF-CBT is a well-established evidence-based treatment for PTS and other symptoms subsequent to child maltreatment and, therefore, is a suitable intervention for this trial. Sixty (60) maltreated youth (ages 6-17) displaying elevated PTS will be assigned to receive TF-CBT or TF-CBT+AAT using a blocked randomization procedure. The TF-CBT protocol is the standard 12 90-minute sessions typically used in research trials. Youth in the TF-CBT+AAT condition will receive the standard protocol with a certified service dog present in the room for each session and the youth will be allowed to interact with the dog during session. A pre-post design will be used to ascertain whether the addition of AAT prompts greater PTS reduction as well as greater improvements in other outcomes, including internalizing symptoms, externalizing symptoms, and emotion regulation. Outcome metrics include caregiver and youth- reported objective measures, and respiratory sinus arrhythmia (RSA) assessed via an electrocardiogram (ECG) during both a resting and stress reactivity paradigm. Feasibility metrics assessed include treatment satisfaction, ability to implement the TF-CBT components with a dog in the room, treatment disrupting events attributable to the dogs, and whether the dogs experienced significant stress as a result of their participation. Stress experienced by the dog will be determined through RSA, salivary cortisol, and behavioral responses. Two prominent hypotheses regarding the mechanism of effect for AAT will be examined. First, therapeutic rapport will be assessed at multiple increments to determine whether the presence of the dog improved the quality or efficiency of development of rapport. Second, RSA will be recorded for the youth during treatment sessions to determine if the presence of the dog yielded a lower intensity of stress during the sessions. Both therapeutic rapport and level of in-session stress will be examined as mediating variables to determine whether either explained enhanced treatment outcomes. To improve the methodological rigor of the study, data will be collected by research assistants blinded to the youth's treatment condition and the same clinicians will implement both treatment conditions, thereby eliminating clinician-specific effects on outcomes.